Implantable defibrillation systems are known in the art which deliver a high-voltage defibrillation pulse to the heart when the onset of fibrillation is detected and/or in the event of a detected complete loss of cardiac output. Such known devices are also capable, if the heart exhibits an arrhythmia such as atrial fibrillation, atrial flutter or tachycardia, or ventricular tachycardia, of cardioverting the heart by delivering a low-voltage pulse in an attempt to regain synchronous operation of the heart, instead of delivering the high voltage defibrillation pulse. In known devices of this type, it would be desirable to provide a compact, efficient device to alert the patient that his implanted device needs attention or is about to defibrillate.
It is known from U.S. Pat. No. 4,086,916 to Freeman at al., for example, to contain a cardiac monitoring system in a wristwatch worn by a patient, the system including circuitry for detecting an erratic heartbeat, a missing pulse or other irregularities and providing an alarm indication, audio and visual, when such an event is detected.
An implantable pacing system is disclosed in U.S. Pat. No. 4,102,346 to Fulker which includes an alarm device as part of the implanted unit which generates an alarm signal to inform the pacemaker user when the battery source of power of the pacemaker is nearing end of life or is malfunctioning.
An implantable tissue stimulating device is disclosed in U.S. Pat. No. 4,345,603 to Schulman which activates an alarm which informs the patient in whom the system is implanted that the battery is in need of replacement. After the user has been so informed, the user applies a magnet externally in the vicinity of the implanted unit to deactivate the monitoring system and thereby cease the continued operation of the alarm.
A pacemaker for controlling tachycardia is disclosed in U.S. Pat. No. 4,407,289 to Nappholz et al. also disclosing means for informing a pacemaker user of the remaining battery life. The user places a magnet externally in the vicinity of the implanted unit, which thereby causes the implanted unit to generate two pulses which can be seen on the patient's ECG waveform. The time separation between the two pulses indicates the remaining battery potential. Application of the magnet, after the pulses have been generated, temporarily disables the device.
In U.S. Pat. No. 5,190,034 to Sholder, an implantable arrhythmia treatment system is disclosed which includes reliable protection against the release of unneeded treatment pulses, that is, which provides protection against a false-positive output. The disclosed system utilizes an alarm generator which may be disposed in the implanted unit, or in an external unit. The alarm may be of any type which does not require constant, active monitoring by the user, such as a sensory alarm, for example, an audio alarm generator or a tactile alarm generator or "tickler".
Other examples of implantable arrhythmia devices which include an alarm generator, either audio, tactile, or visual, are found in U.S. Pat. Nos. 4,295,474 to Fischell; 4,210,149 to Heilman et al.; and 3,783,877 to Bowers.
According to the current state of the art, error conditions are typically announced within an implantable cardioverter defibrillator (ICD) using a piezo annunciator or beeper. The current Eagle Model 2800 in development by Pacesetter, Inc., A St. Jude Medical Company of Sylmar, Calif., for example, utilizes a piezo actuator to flex the titanium can at audio frequencies. However, in some instances, the efficacy of audio emissions from devices implanted abdominally can be questioned. The attenuation of the audio transmitted through tissue is dramatic and aged patients commonly have hearing loss that further decreases their sensitivity to implanted audio generators.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.